The present invention relates to a mechanism for controlling the working movement of the weft-carrying grippers in weaving looms with continuous weft feed, said mechanism providing remarkable advantages compared to the technical solutions so far adopted for this purpose.
As is known to those skilled in the art, it is very difficult to obtain -- in continuous weft feed looms, using weft-carrying grippers which move forward and backward through the shed -- a working movement of such grippers which may answer the many actual requirements, often in contrast with one another, having to be satisfied; and it cannot be said that the mechanisms controlling said movement, which have so far been provided by known techniques, are adopted to satisfactorily solve the various problems, which have to be faced by the manufacturers of weaving looms.
When undertaking the studies, which have led to the present invention, it seemed necessary to establish first of all which were the main requirements having to be satisfied by the mechanism for controlling the gripper movement, which had to be realized with more rational principles than in the past. Now that such a mechanism has been successfully conceived, it will be convenient to sum up said requirements hereunder, so that the characteristics and the scope of the present invention may be properly understood and correctly valued.
From the point of view of the gripper movement to be obtained, it is hence necessary:
TO BE ABLE TO LIMIT THE SPEED OF THE CARRYING GRIPPER, AT THE INSTANT WHEN IT GRIPS THE WEFT THREAD IN PROXIMITY TO ONE END OF THE SHED;
TO BE ABLE TO LIMIT THE SPEED OF THE DRAWING GRIPPER, AT THE INSTANT WHEN IT ABANDONS THE WEFT THREAD IN PROXIMITY TO THE END OF THE SHED OPPOSITE TO THAT IN WHICH THE THREAD IS BEING GRIPPED;
FOR THE GRIPPERS TO BE OUT OF THE SHED, WHEN THE REED BEAT-UP TAKES PLACE;
FOR THE GRIPPERS TO ENTER THE SHED ONLY WHEN THE LATTER, FORMED BY THE WARP YARNS, IS SUFFICIENTLY OPEN (IN ORDER TO PREVENT THE GRIPPERS, WEDGING IN AMONG THE STRETCHED YARNS, FROM CAUSING BREAKS IN THE WARP);
TO REDUCE THE ACCELERATIONS OF THE GRIPPERS, IN ORDER TO LIMIT THE TENSION OF THE WEFT THREAD DURING ITS INSERTION, AND TO FURTHER REDUCE THE DYNAMIC STRESSES ON THE MECHANICAL MEMBERS WHICH CONTROL THE MOVEMENT OF THE GRIPPERS;
FOR THE ELASTIC YIELDINGS AND THE SLACKS OF THE MECHANISM CONTROLLING THE MOVEMENT OF THE GRIPPERS TO BE AS SMALL AS POSSIBLE;
FOR THE RECIPROCATING MOTION MASSES OF THE HERETOFORE SPECIFIED MECHANISM -- AND HENCE THE INERTIAL LOADS AND THE VIBRATORY PHENOMENA DERIVING THEREFROM -- TO BE AS LIMITED AS POSSIBLE.
In connection with this point, which is particularly important, it should not be frogotten that the essential condition for the correct working of continuous weft feed looms (without shuttles), is to be able to operate a precise weft thread exchange, between the carrying gripper and the drawing gripper, close to the center line of the fabric (at the center of the shed). Now, the slacks of the insertion mechanism and the elastic stretches due to the inertial loads acting on its members, determine an additional elastic elongation of the stroke of the grippers, in respect of the stroke which would be had if the mechanism were to be considered as perfectly rigid. This elastic elongation is obviously a function of the speed of the weaving machine; whereby, with the varying of the mechanism speed, varies the relative position of the carrying gripper in respect of the drawing gripper, close to the center line of the fabric, where the weft exchange takes place. Consequently, the difficulty arises of an exact adjustment -- to be performed with the machine at a stop -- of the grippers' stroke, in that it is necessary to reckon exactly the addtional elastic elongation of the stroke itself. If said reckoning is not correct, the grippers will end by performing -- at a steady speed rate of the machine -- a shorter or a longer stroke in respect to that which would determine the best weft exchange conditions; in the first case, the exchange may not take place or it may be faulty; in the second case, there may be a true and proper collision between the two grippers, with obviously disastrous consequences. The described phenomenon is particularly felt in the transient starting stage of the machine, since in this stage, the speed varies from naught to a steady speed rate, and with it varies also the additional elastic elongation of the grippers' stroke.
On the other hand, a rationally conceived mechanism for controlling the grippers' movement, has to satisfy requirements from the constructive and economical point of view, as well as from the point of view of practical industrial use, the main among said requirements being:
the possibility to weave, on a same loom, fabrics of different width; this requirement implies the need to be able to adjust -- in an easy and quick way, and on a same loom -- the distance moved by the grippers from one end to the other of their stroke;
the economical opportuneness for a single type of control mechanism to be suitable both for weaving machines adapted to weave only narrow fabrics, and for weaving machines adapted to weave fabrics of considerable width; and moreover, that a same mechanism of this type may be mounted on said different machines with the smallest possible number of modifications; if said requirement is satisfied, it is in fact possible to increase the range of looms being constructed, to reduce the planning, construction, storage and service expenses, and to achieve a greater standardization in the industry;
the opportuneness of having a noiseless mechanism. It is in fact known that, in the weaving machines of the type in question, the main cause for noise is provided by the weft insertion mechanism; whereby, the noise in weaving rooms is at present extremely high, and it is responsible for poor working conditions and for considerable psychophysical stresses on the operators;
the advantage of having a relatively small mechanism, allowing to limit the dimensions of the loom, and hence the space occupied by the same in weaving rooms;
the advantage of making a mechanism with a high mechanical efficiency, so as to reduce the electrical input of the weaving machine.
In general, the machanisms for controlling the working movement of the grippers, known so far, are made with articulated systems consisting of crank gears and linkages, or else with cams. The articulated systems have the considerable drawback of not being apt to provide the movement of the grippers with the desired characteristics, particularly as far as the acceleration of the grippers is concerned. The solutions with cams, so far adopted, provide for the use of cams which allow a limited stroke of the cam follower and hence demand a further amplification mechanism, to proportion the stroke of the cam follower to the stroke of the grippers.
In this case, there are considerable stresses on the cam follower roller contacting the cam surface profile; moreover, the amplifying mechanism -- especially on machines adapted to weave the wide fabrics -- introduces slacks and inertial masses in reciprocating motion, which increase the loads, limit the speed of the mechanism and cause highly troublesome noises.
The mechanism for controlling the grippers movement according to the present invention, is adapted to eliminate the various drawbacks of known mechanisms and to satisfy, in a very efficient way, all the requirements set forth hereabove, said mechanism adopting an original constructive arrangement for turning a rectilinear reciprocating motion into a rotary, also reciprocating motion.